The objective of this research is to study the biochemical and physiological changes in selenium deficient subhuman primates, using 12 selenium depleted pregnant Rhesus monkeys. Four of these will be fed a basal diet (with casein, soybean meal and torula yeast as the protein sources) with additions of 0.2 ppm selenium. The remaining eight monkeys will be fed the selenium deficient basal diets containing either casein, soybean meal plus torula yeast (30 ppb Se), or soybean meal plus torula yeast (15 ppb), or just torula yeast (15 ppb) as the protein sources. Blood will be taken at monthly or bimonthly intervals from both the adult and young monkeys for selenium and vitamin E analyses, and for enzyme assays. Measurements of erythrocyte glutathione peroxidase activity, plasma glutamicoxalacetic transaminase, lactic dehydrogenase, creatine phosphokinase, and ornithine carbamyl transferase activities are planned on each blood sample. Complete blood counts and SMACs (panel of 18 blood chemistries) will also be done as deemed necessary. Muscle and liver biopsies will be taken from the infant monkeys after weaning, and glutathione peroxidase and glutathione transferase activities will be determined on the tissues. In vitro Se-75 uptake by erythrocytes will also be studied.